Investigation of the details of the loss of the two methyl groups at C4 in the biosynthesis of cholesterol from lanosterol will be continued. Experiments involving treatment of synthesized model substrates with rat liver homogenate will be used to explore further the structural requirements for substrates for oxidative demethylation. Studies will also be continued on laboratory simulation of the oxidative demethylation at C4. Initial efforts will be directed toward improving the yield and efficiency of the recently discovered direct functionalization of the C4 beta methyl group via photolysis of a C3 doxyl derivative. Exploration of this new method of oxidizing saturated centers in other steroidal contexts is envisaged. Experiments are also planned on more nearly biomimetic methods of hydroxylating the C4 methyl groups.